1. Field of the Invention
This invention relates to wings for fitment-constrained air vehicles, and more particularly to wings for tube and pylon launched missiles, projectiles and unmanned aerial vehicles (UAVs).
2. Description of the Related Art
Air vehicles such as missiles, projectiles and unmanned aerial vehicles (UAVs) are often launched from ground, air or sea based tube or pylon launch platforms. These vehicles range from a fraction of a pound for small UAVs to upwards of 10,000 pounds for large cruise missiles and munitions, and fly with speeds ranging from a few miles per hour to transonic, i.e. around Mach 1. These launch platforms are “fitment” constrained in space and volume e.g. the limited volume of a tube or the limited volume inside or under an airframe. To utilize the available space and volume, these vehicles typically employ retractable wings 10 that are stored inside the airframe 12 and deploy at launch as shown in FIGS. 1a and 1b. As used herein a “wing” is any aerodynamic surface that provides flight control and/or lift generation including wings, fins and canards.
Retractable wings are typically formed of machined aluminum. Machined aluminum wings can withstand the heavy loads imparted by transonic flight and/or rapid maneuvering. Machined aluminum is also easily machined to satisfy close tolerances on the “outer mold line” (OML) of the wing. A tight OML tolerance is critical to provide minimal disturbance in aerodynamic performance that could create roll/pitch moments, drag, Etc. However, the wings are limited to have a ‘chord’ length “d” less than the diameter of the vehicle and a span length “l” less than the length of the air frame in order to fully retract inside the air frame for storage.
As customer demands on the performance of these types of air vehicles increases and the fitment constraints are restricted further, the limitations on chord and span lengths provide inadequate endurance (range) and control to fly desired missions. By comparison, commercial manned aircraft typically have a chord length that 3×-4× the diameter of the airframe and a span length of 2× the length of the of the air frame to provide sufficient wing surface area to provide lift at low speeds for efficient flight and maneuverability.
Inflatable wings have been around and in limited use for about 40 years. Inflatable wings have been proposed for use in an inflatable escape plane for pilots and high-altitude high-endurance UAVs launched from space. These aerial vehicles are slow moving and precise control is not required. In high altitude loiter (HAL) vehicles the wing is folded and stored in a wing-box inside the airframe. To deploy, the wing-box jack knifes from the airframe and a gas canister inflates a skin around and attached to the wing-box. The skin inflates to a shape having the OML of the wing. The inflated wing can have a chord and/or span length larger than the fitment constraint of the airframe and a much larger total surface area. On the inflatable escape plane the entire plane inflates.
Inflatable wings are feasible for these limited applications in which high-speed, precise control and high wing loads are not required. However, despite considerable investment and prolonged efforts the industry has failed to produce an inflatable wing suitable for use in air vehicles such as the tube or pylon launched missiles, projectiles and general use UAVs. The primary issue being that the tolerance on the OML provided by inflating a bag is not good enough, typically no better than ¼ inch. For high speed vehicles with high wing loads and precise terminal flight performance requirements, the aerodynamic performance of inflatable wings is insufficient. The industry has tried different approaches to improve the OML tolerance including baffles in the skin and segmented inflatable wings, but to no avail. Furthermore, the gas-filled skin is not strong enough to withstand heavy loading. Even with its limitations on chord and span length, retractable aluminum wings remain the only viable solution for the fitment constrained air vehicles commonly used for missiles and munitions.